Technical Note Experimental Study on Scour around a T-Shaped Spur Dike in a Channel Bend Mohammad Vaghefi 1 ; Masoud Ghodsian 2 ; and Seyed Ali Akbar Salehi Neyshabouri 3 Abstract: This paper deals with the study of the geometry of the scour hole and topography of the bed around a T-shaped unsubmerged spur dike located in a 90° bend. The experiments were carried out in a channel with a 90° bend. Uniform sediments having an average diameter of 1.28 mm were used under clear-water scour conditions. The effects of parameters like the length of a spur dike, the wing length of a spur dike, the location of a spur dike in the bend, the radius of bend, and flow intensity on the scour around a T-shaped spur dike were investigated. A new equation for scour parameters at a T-shaped spur dike is developed. DOI: 10.1061/(ASCE)HY.1943-7900.0000536. © 2012 American Society of Civil Engineers. CE Database subject headings: Channels; Scour; Levees; Dikes; Experimentation. Author keywords: Bend; Depth of scour; Local scour; T-shaped spur dike. Introduction Spur dikes are hydraulic engineering structures for preserving the desired water depth, deflecting the main current in the rivers, and protecting river banks. Protrusion of spur dykes to a channel leads to significant changes of flow patterns and bed configura- tions. These changes bring either disasters primarily in terms of excessive scouring or benefits such as improvement of morphologi- cal diversities. In river restoration, for example, desired flow and morphology are generally expected when spur dykes are effectively arranged. When a spur dike is located in the outer bank of a bend, the scour process is a complex phenomenon. Despite their abundant use, the spur dikes located at the bends of rivers have witnessed few comprehensive studies. For example Przedwojski (1995), Mesbahi (1992), and Fazli et al. (2007) experimentally studied the influence of some of the important parameters on the maximum scour depth. In addition, Tingsanchali and Maheswaran (1990), Soliman et al. (1997), Giri and Shimizu (2004), Ghodsian and Mousavi (2004), and Forghani et al. (2007) examined the scour pattern around the spur dikes located in a bend. Review of the literature shows that almost all the investigators have studied the scour around the straight spur dike. Moreover, there is a lack of information, to the knowledge of authors, about the scour at a T-shaped spur dike in a bend. Ghodsian and Vaghefi (2009) reported the results of experiments on flow field and to a lesser extent to scour because of a T-shaped spur dike located at section 75° in a bend. Vaghefi et al. (2009) studied the effect of length of a T-shaped spur dike on scour. Unfortunately, there are very few quantitative information and systematic studies on scour because of spur dykes located in a bend. Compared with bridge piers and abutments, research on a spur dike still await ex- ploration, especially when it is located at different locations in a channel bend. In spite of the use of a spur dike at different locations of a river bend, there is little information about the effect of impor- tant parameters on the scour because of a T-shaped spur dike. This paper examines the effects of the location of the spur dike in the bend, the length of spur dike, the wing length of spur dike, and flow intensity on the scour and bed topography around a T-shaped spur dike located in a 90° bend. Dimensional Analysis Fig. 1 represents the geometric characteristics of the scour hole be- cause of a T-shaped spur dike. If ϕ represents the maximum dimen- sions of scour hole parameters (maximum depth of scour d sm , upstream length of scour hole c, width of scour hole a, and down- stream length of scour hole d), using dimensional analysis, one can write (see Fig. 1) φ Y ¼ f  θ 90 ; V V c ; L B ; 1 L ; R c B ; L d 50  ð1Þ in which L = length of spur dike; λ = wing length of spur dike; θ = location of spur dike in the bend in degrees; Y = approach depth of flow; B = channel width; d 50 = median size of bed material; R c = radius of channel bend; V c = critical velocity of sediment; V = approach flow velocity; and g = acceleration because of grav- ity. Ghodsian and Vaghefi (2009) showed dependency of L∕B and λ∕L on the depth of scour. They showed that by increasing L∕B, the depth of scour increases, and by increasing λ∕L, the depth of scour decreases. Experiments Experiments were carried out at the Hydraulic Laboratory of Tarbiat Modares University, Tehran, Iran. The main channel con- sisted of a 7.1 m long upstream and a 5.2 m long downstream straight reach. A 90° channel bend was located between the two 1 Assistant Professor, Dept. of Civil Engineering, Persian Gulf Univ., Bushehr, Iran. E-mail: vaghefi@pgu.ac.ir. 2 Professor, Water Engineering Research Institute, Tarbiat Modares Univ., Tehran, Iran (corresponding author). E-mail: ghods@modares.ac.ir 3 Professor, Water Engineering Research Institute, Tarbiat Modares Univ., Tehran, Iran. E-mail: salehi@modares.ac.ir Note. This manuscript was submitted on April 22, 2008; approved on November 17, 2011; published online on April 16, 2012. Discussion period open until October 1, 2012; separate discussions must be submitted for individual papers. This technical note is part of the Journal of Hydraulic Engineering, Vol. 138, No. 5, May 1, 2012. ©ASCE, ISSN 0733-9429/ 2012/5-471–474/$25.00. JOURNAL OF HYDRAULIC ENGINEERING © ASCE / MAY 2012 / 471 J. Hydraul. Eng. 2012.138:471-474. 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